Polyvinyl chloride resins are processed for shaping by blending a stabilizer of calcium-zinc base, barium-zinc base, or the like therein, and shaped articles thereof are widely used as products suitable for general use and further for foods, medical use, and the like.
However, since these stabilizers have abilities insufficient to inhibit heat deterioration of the polyvinyl chloride resins, they used to have disadvantages, such as impairing initial colorability of the shaped articles and having insufficient thermal stability while being shaped. Therefore, as a means for improvement of these disadvantages, polyvinyl chloride resin compositions are proposed to which an antioxidant is added or a compound having a hydroxyl group is added.
Patent Document 1 (JP 50-92947A) discloses a method of adding calcium soap, zinc soap, polyol or a derivative thereof, and a neutral inorganic calcium salt to a chloride-containing resin.
Patent Document 2 (JP 54-81359A) discloses a method of adding a water soluble polymer to a chloride-containing polymer.
Patent Document 3 (JP 57-147552A) discloses a method of adding a condensation reaction product of dipentaerythritol and dicarboxylic acid, zinc oxide, zinc carbonate or fatty acid zinc, and hydrotalcite to a chloride-containing resin.
Patent Document 4 (JP 60-238345A) discloses a method of adding a saponified product of an ethylene-vinyl acetate copolymer, having an ethylene unit content of from 20 to 50% and having a degree of saponification of a vinyl acetate unit of 96% or more, and a hydrotalcite-based compound to a thermoplastic resin.
Patent Document 5 (JP 1-178543A) discloses a method of adding metal soap and a saponified product of an ethylene-vinyl acetate copolymer having a copolymer composition that has an ethylene content of from 20 to 75 mol % and has a degree of saponification of a vinyl acetate portion of 50 mol % or more to a halogen-containing thermoplastic resin.
Patent Document 6 (JP 6-287387A) discloses a method of adding a metal salt of an organic acid and acetalized polyvinyl alcohol to a vinyl chloride-based resin.
Patent Document 7 (JP 9-3286A) discloses a method of adding partially saponified polyvinyl alcohol having a degree of saponification of from 70 to 95 mol %, having an average degree of polymerization of from 300 to 2000, and having a terminal mercapto group to a vinyl chloride-based resin.
Patent Document 8 (JP 9-31281A) discloses a method of adding a zinc compound, hydrotalcites, polyvinyl alcohol, and polymethyl methacrylate to a vinyl chloride-based resin.
Non-Patent Document 1 (Japanese Journal of Polymer Science and Technology Vol. 47, No. 3, 197 (1990)) discloses a method of adding zinc stearate-calcium stearate complex soap and completely saponified polyvinyl alcohol having a degree of polymerization of 600 or more to polyvinyl chloride.
Non-Patent Document 2 (Japanese Journal of Polymer Science and Technology Vol. 47, No. 6, 509 (1990)) discloses a method of adding zinc stearate-calcium stearate complex soap and partially saponified polyvinyl alcohol having a degree of polymerization of 500 and having a degree of saponification of 73.6 mol % to polyvinyl chloride.
Non-Patent Document 3 (Japanese Journal of Polymer Science and Technology Vol. 50, No. 2, 65 (1993)) discloses a method of adding zinc stearate-calcium stearate complex soap and an ethylene-vinyl alcohol copolymer having an ethylene content of 29 mol % or more to polyvinyl chloride.
Non-Patent Document 4 (Polymers & Polymer Composites, Vol. 11, 649 (2003)) discloses a method of adding zinc stearate-calcium stearate complex soap, and polyvinyl alcohol having a degree of polymerization of 500 and having a degree of saponification of 98.5 mol % or an ethylene-vinyl alcohol copolymer having an ethylene content of 29 mol % or more to polyvinyl chloride.
Non-Patent Document 5 (Journal of the Adhesion Society of Japan Vol. 43, No. 2, 43 (2007)) discloses a method of adding polyvinyl alcohol having a degree of polymerization of 500 and having a degree of saponification of 88 mol % or polyvinyl alcohol having a degree of polymerization of 1700 and having a degree of saponification of 78 mol % or more, and polymethyl methacrylate to polyvinyl chloride.
However, the polyvinyl chloride resin compositions described in Patent Documents 1 through 8 and Non-Patent Documents 1 through 5 have problems of not being sufficient in the long term thermal stability and of being colored.